database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-30 11:03:19 +03:00
Code Activity

Use posix_fallocate() for new WAL files, where available.

Browse Source 
This function is more efficient than actually writing out zeroes to
the new file, per microbenchmarks by Jon Nelson. Also, it may reduce
the likelihood of WAL file fragmentation.

Jon Nelson, with review by Andres Freund, Greg Smith and me.
This commit is contained in:
Jeff Davis
2013-07-05 12:30:29 -07:00
parent 8800d8061d
commit 269e780822
5 changed files with 67 additions and 37 deletions
Download Patch File Download Diff File Expand all files Collapse all files

93
src/backend/access/transam/xlog.c
View File

@ -2256,11 +2256,9 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
{
char path[MAXPGPATH];
char tmppath[MAXPGPATH];
char *zbuffer;
XLogSegNo installed_segno;
int max_advance;
int fd;
int nbytes;
XLogFilePath(path, ThisTimeLineID, logsegno);
@ -2294,16 +2292,6 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
unlink(tmppath);
/*
* Allocate a buffer full of zeros. This is done before opening the file
* so that we don't leak the file descriptor if palloc fails.
*
* Note: palloc zbuffer, instead of just using a local char array, to
* ensure it is reasonably well-aligned; this may save a few cycles
* transferring data to the kernel.
*/
zbuffer = (char *) palloc0(XLOG_BLCKSZ);
/* do not use get_sync_bit() here --- want to fsync only at end of fill */
fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
S_IRUSR | S_IWUSR);
@ -2312,38 +2300,73 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m", tmppath)));
/*
* Zero-fill the file. We have to do this the hard way to ensure that all
* the file space has really been allocated --- on platforms that allow
* "holes" in files, just seeking to the end doesn't allocate intermediate
* space. This way, we know that we have all the space and (after the
* fsync below) that all the indirect blocks are down on disk. Therefore,
* fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
* log file.
*/
for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
#ifdef HAVE_POSIX_FALLOCATE
{
errno = 0;
if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
{
int save_errno = errno;
errno = posix_fallocate(fd, 0, XLogSegSize);
/*
* If we fail to make the file, delete it to release disk space
*/
unlink(tmppath);
if (errno)
{
int errno_saved = errno;
close(fd);
/* if write didn't set errno, assume problem is no disk space */
errno = save_errno ? save_errno : ENOSPC;
unlink(tmppath);
errno = errno_saved;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to file \"%s\": %m", tmppath)));
errmsg("could not allocate space for file \"%s\" using posix_fallocate: %m",
tmppath)));
}
}
pfree(zbuffer);
#else /* !HAVE_POSIX_FALLOCATE */
{
/*
* Allocate a buffer full of zeros. This is done before opening the
* file so that we don't leak the file descriptor if palloc fails.
*
* Note: palloc zbuffer, instead of just using a local char array, to
* ensure it is reasonably well-aligned; this may save a few cycles
* transferring data to the kernel.
*/
char *zbuffer = (char *) palloc0(XLOG_BLCKSZ);
int nbytes;
/*
* Zero-fill the file. We have to do this the hard way to ensure that
* all the file space has really been allocated --- on platforms that
* allow "holes" in files, just seeking to the end doesn't allocate
* intermediate space. This way, we know that we have all the space
* and (after the fsync below) that all the indirect blocks are down on
* disk. Therefore, fdatasync(2) or O_DSYNC will be sufficient to sync
* future writes to the log file.
*/
for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
{
errno = 0;
if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
{
int save_errno = errno;
/*
* If we fail to make the file, delete it to release disk space
*/
unlink(tmppath);
close(fd);
/* if write didn't set errno, assume no disk space */
errno = save_errno ? save_errno : ENOSPC;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to file \"%s\": %m",
tmppath)));
}
}
pfree(zbuffer);
}
#endif /* HAVE_POSIX_FALLOCATE */
if (pg_fsync(fd) != 0)
{